Where Does the Quantum World End and Ours Begin?

Quantum mechanics may be one of the most precisely tested paradigms in science, but there’s still no universally accepted interpretation of what it tells us about reality. How do we get from the wave-like behavior of quantum systems to the solid, macroscopic world of objects and the universe at large? Jonathan Halliwell, a professor of theoretical physics at Imperial College London, has spent his career probing the foundations of quantum theory.

In this episode, he tells Steven Strogatz why decoherence — the process by which fragile quantum behavior becomes dispersed through interactions with the surrounding environment — is key to the transition from quantum to classical behavior, and he describes the “histories” approach that he uses to understand this. Along the way, Halliwell tackles some of the field’s deepest paradoxes. He explains why the quantum-to-classical transition doesn’t require a conscious observer, and he explores Einstein’s famous question of whether the moon is really there when no one looks.

The conversation ends with Halliwell explaining how yoga and meditation help him sit with the mystery of competing perspectives in science. Listen on Apple Podcasts, Spotify, TuneIn or your favorite podcasting app, or you can stream it from Quanta. STEVE STROGATZ: Alright, here we go.

LEVIN: A podcast from Quanta Magazine where we explore some of the biggest unanswered questions in math and science today. STROGATZ: Yes, Janna, big questions. Today we got one of the biggest of all.

LEVIN: Okay, I’m excited. STROGATZ: Yeah, brace yourself and buckle up. This is about foundations of quantum mechanics, one of the really paradoxical things that a lot of people worry about.

LEVIN: Yeah, it really is the great unsolved quandary. Quantum mechanics, the most precisely tested paradigm in all of science to the largest number of decimal points, and still there’s no coherent interpretation. I don’t know anyone who’s gonna claim to understand quantum mechanics fully.